Both in humans and in rats dopaminergic drugs in small doses facilitate male sexual behavior. The goals of the proposed are to localize within the brain the site(s) of this facilitation, to determine more specifically the copulatory components most affected, to explore whether intracranial infusion of a dopamine (DA) agonist can retard the decline in sexual behavior following castration, and to indicate whether these effects are mediated by DA receptors. Three sites of dopaminergic (DA) synapse seem important candidates for DA's facilitation of masculine behavior. 1) The caudal putamen (CP) is primarily concerned with motor patterns; since masculine behavior is a very active motor pattern, it has been thought that the CP may be important for its expression. 2) In the nucleus accumbens (NA), DA turnover is affected by castration and subsequent hormone replacement; this relationship between testosterone and DA in the NA suggests a role for this site in masculine function. 3) The medial preoptic area (MPOA) is the major site at which testosterone can elicit masculine behavior; it also receives a very small DA projection. Preliminary data from our lab suggest that it may be the principal site of DA facilitation of male sexual behavior. Experiments 1A, 1B, and 1C will investigate the effects of intracranial infusions of apomorphine (APO), a DA agonist, into the MPOA, the CP, and the NA, respectively. Various components of masculine behavior will be analyzed separately, in order to determine the relative drug effects on sexual arousal and on copulatory mechanisms. Experiment 2 will determine whether infusions of APO into MPOA, CP, or NA will restore components of sexual behavior after castration. Systemic APO has been reported to increase the numbers of castrated males copulating. We wish also to analyze the specific behavioral components affected. Experiment 3 will indicate whether the effects observed in Experiments 1 and 2 are mediated by DA receptors. We will pretreat with the DA antagonist pimozide, using a regimen previously shown to block the effects of systemically administered APO on sexual behavior. Long term goals include specification of DA receptor mechanisms mediating the observed effects and exploration of interactions of DA with other transmitters in the regulation of masculine sexual behavior. A better understanding of the transmitters and circuitry of masculine function should improve treatment of sexual dysfunction.